Mécanismes moléculaires de la compartimentation des métaux chez les cellules végétales – DISTRIMET

Background Transition metals are essential for many functions in living cells. They are required for electron transfer reactions during respiration and photosynthesis which take place in specific intracellular organelles: mitochondria and chloroplasts. On the other hand, due to their physico-chemical properties, transition metals become toxic to living cells when their concentration in the cytosol rises. Hence, metals need to be safely stored or sequestered in intracellular compartments in which they become harmless. The compartmentalization of transition metals needs to be tightly controlled to prevent them from causing damage to cells while allowing access to their active sites. This project addresses the issue of metal distribution in plant cells. Plant metal nutrition impacts crop yields on soils with limiting metal availability. Crop metal content, in turn, impacts nutritional quality and food safety for human and cattle. The mechanisms of metal absorption by plant roots have been extensively studied and molecular pathways that control Fe and Zn uptake in model and crop species have been unraveled. In contrast, relatively few studies have dealt with metal compartmentalization in plant cells. The mechanisms responsible for Zn sequestration into the vacuole and for Cu distribution in chloroplast are just beginning to be elucidated. Plant cells represent a good model for the study of intracellular metal distribution: they contain large intracellular vacuoles responsible for metal storage and sequestration and chloroplasts that are the main site where transition metals such as Fe and Mn are required for photosynthetic function. This project will specifically address the issue of Fe and Mn storage and distribution between plant cell vacuole and chloroplasts. Experimental plan The partners involved in the project have complementary expertise that will allow successful achievement of the aims of the project. Partner 1 has recognized expertise in intracellular metal transport and vacuole biogenesis in plant cells. Partner 2 is a world leading group in the field of iron homeostasis and elucidated the molecular basis for Fe uptake by plants and Fe storage in plant chloroplast. Associated groups provide expertise in elemental imaging techniques based on synchrotron radiation that will allow 3-D mapping of metal distribution in plant cells. The different partners will provide an optimal combination of cutting edge expertise in Arabidopsis molecular genetics, elemental mapping and cell biology. The project has three major goals: - Identify novel players involved in metal distribution in plant cells The metal transporters that allow uptake of Fe and Mn into chloroplasts remain to be identified. In addition, metal storage and mobilization in vacuoles is far from being completely understood. These questions will be addressed through molecular genetic analysis and subcellular localization of candidate metal transport proteins. - Decipher the mechanisms of iron mobilization during seed germination and its regulation Seed germination provides an excellent example of developmentally regulated metal mobilization. We will therefore investigate the distribution of metals in germinating Arabidopsis seeds impaired in metal mobilization or storage. As the vacuole is a central metal storage site, the dynamics of vacuole remodelling in germinating seeds will be studied in parallel. The project aims at identifying regulatory mechanisms by studying the cross talk between iron mobilization and iron storage proteins and by screening for mutants impaired in these processes. - Analyze the dynamics of metal distribution in leaves during stress responses Leaves will serve as an example to study metal redistribution triggered by environmental cues. We will investigate the relocation of metals within cells upon several stresses. The importance of the changes in metal distribution will be investigated by testing stress tolerance in mutants impaired in metal compartmentalization. Expected output The project will provide an integrated view of the distribution of metals in plants at the cell and tissue levels. Concomitantly, it will increase our knowledge of vacuole biogenesis and plasticity during development. The project will identify proteins responsible for metal partitioning and storage between organelles and investigate the mechanisms that regulate their expression and function. Moreover, this project will be conducive to the development of elemental mapping in biological material. The study of metal mobilization in seeds will provide extensive knowledge to address the problem of iron bioavailability in crops in the future. This issue is crucial to fight iron deficiency in human population(s). Simultaneously, the analysis of the role of metal redistribution in leaf cells in response to stresses will be useful to improve plant resistance and improve plant yield in sub optimal conditions.